Spin-state differences and spin crossover in five-coordinate Lewis base adducts of cobalt(II) Schiff base complexes. Structure of the high-spin (N,N'-o-phenylenebis(salicylaldiminato))cobalt(II)-2-methylimidazole adduct
TL;DR: C 24 H 20 CoN 4 O 2 cristallise dans P2 1 /n avec Z=4; affinement jusqu'a R=0,062.
Abstract: C 24 H 20 CoN 4 O 2 cristallise dans P2 1 /n avec Z=4; affinement jusqu'a R=0,062. Coordination pyramide carree deformee
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TL;DR: Tetracoordinated metal-chelate complexes with six-membered metallocycles as discussed by the authors have been shown to be stable in the presence of tautomeric forms of the ligands.
545 citations
TL;DR: In this article, the Bragg and Williams approximation of the Ising model is used to describe spin-state transitions in metal complexes which are driven by a change of temperature T or pressure p are always associated with a considerable reorganization of molecular geometry, the change involves metal-ligand bond lengths R, bond angles and a variation of ligand orientation.
Abstract: Spin-state transitions in metal complexes which are driven by a change of temperature T or pressure p are always associated with a considerable reorganization of molecular geometry. The change involves metal-ligand bond lengths R, bond angles, and a variation of ligand orientation. In particular, the elongation 4R by up to ∼ 10% occurring in the course of the LS → HS conversion produces an expansion of molecular volume ΔV ≌ 25 A3 per metal atom. The average crystal structure for given values of T and p is reproduced by the fractional occupancy of the individual structures of the high-spin (HS) and low-spin (LS) isomer. The transitions are reasonably well described by a number of theoretical models which are equivalent to the Bragg and Williams approximation of the Ising model. The dynamics of the spin-state transitions in solution, based on measurements by ultrasonic and photo-perturbation techniques, is in general rapid with rate constants between 4 × 105 and 3 × 108 s−1. Similar results are obtained for the spin conversion in solid complexes where the line shape analysis of Mossbauer spectra based on the theory of Blume and Tjon is applied. The dynamics may be rationalized employing one-dimensional cross sections through Gibbs free-energy surfaces G = G(R), an alternative being the comparison of the results with quantum-mechanical calculations for a radiationless non-adiabatic multiphonon process.
361 citations
TL;DR: In this article, the theoretical aspects to be considered when discussing spin-crossover compounds in general and cobalt(II) systems in particular are discussed and case studies on [Co(bpy)3] 2+ and [Co[terpy)2] 2 + are presented and discussing results from magnetic susceptibility measurements, X-ray crystallography, optical spectroscopy, and EPR spectroscopic analysis.
204 citations
Journal Article•
TL;DR: In this paper, a review of spin crossover effects in small polynuclear clusters, particularly dinuclear species, and in extended network molecular materials, some of which have interpenetrated network structures are presented.
Abstract: This review deals with spin crossover effects in small polynuclear clusters, particularly dinuclear species, and in extended network molecular materials, some of which have interpenetrated network structures. Fe(II)Fe(II)species are the main focus but Co(II)Co(II) compounds are included. The sections on dinuclear compounds include short background reviews on (i) synergism of SCO and spin-spin magnetic exchange (ii) cooperativity (memory effects) in polynuclear compounds, and (iii) the design of dinuclear SCO compounds using structural and ligand field concepts. Known examples of dinuclear compounds are reviewed and our new examples are described, these being based on hydrogen-bonded water to pyrazole ligand linkages. Incomplete (half) SCO transitions, due to HS-HS to HS-LS transformations, are commonly observed, with no thermal hysteresis. New and ground-breaking studies of microporous extended network Fe(II)(NCS)2(py)4-type systems reveal reversible host-guest systems which display reversible sorption/desorption of guest molecules and SCO behaviour that varies with exchange of the guests.
179 citations
TL;DR: In this article, a review describes the recent advances made in the syntheses, structures (including the use of synchrotron sources and variable-temperature crystal structures and PXRD determinations of unit cell axes), magnetism, and photomagnetism of dinuclear and 1-D chain spin-crossover compounds of (primarily) iron(II), iron(III) and cobalt(II).
Abstract: This review describes the recent advances made in the syntheses, structures (including the use of synchrotron sources and variable-temperature crystal structures and PXRD determinations of unit cell axes), magnetism, and photomagnetism of dinuclear and 1-D chain spin-crossover compounds of (primarily) iron(II), iron(III) and cobalt(II). It focuses on the work of the author's group and also includes a discussion of related work by other groups. In particular, the early and ongoing work by Kahn, Real, Gutlich and co-workers on bipyrimidine-bridged FeII dinuclear materials has been extended by us and others to include many other new bridging and capping ligands. This had led to a fuller understanding of the spin transitions that involve HS-HS, HS-LS and LS-LS pair states. The same is being achieved for new 1-D chain materials, and notable advances include structural observation of ordered and disordered metal centres and corresponding spin states. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
162 citations